1. Field of the Invention
The present invention relates to an image display apparatus, which is suitably applicable, for example, to head-mounted displays, goggle type displays, etc. designed so as to observe an enlarged image of image information displayed on a reflective liquid-crystal display element as a display element through an optical element having a free curved surface properly set.
2. Related Background Art
A variety of proposals have been made heretofore for the head-mounted image observing apparatus (image display apparatus), which are so called head-mounted displays, in such structure as to permit an observer to observe an enlarged virtual image of the image information displayed on the image display device of liquid crystal or the like, for example, by use of an optical element having an entrance surface, a plurality of reflective surfaces, and an exit surface in surfaces of a transparent material.
For example, Japanese Patent Application Laid-Open Nos. 7-333551, 8-50256, 8-160340, 8-179238 and 8-234137, etc. suggest the image observation apparatus the overall scale of which is decreased by using an LCD (liquid crystal display) as a display means for displaying the image information and using a compact prism as an observation optical system.
FIG. 1 is a schematic diagram of the major part of the image observation apparatus suggested in Japanese Patent Application Laid-Open No. 7-333551. In FIG. 1, light emitted from the LCD 51 is made incident to the entrance surface 53 of compact prism 52. Then the light is folded between a totally reflecting surface 54 with curvature, formed in the compact prism 52, and a reflecting surface 55 and thereafter the light is made to emerge from the compact prism 52 to be guided to the observer E. This results in forming a virtual image of the image information displayed on the display means (LCD) 51 and thus permits the observer E to observe the virtual image. The reflecting surface 55 of the compact prism 52 is comprised of an eccentric, free, curved surface, which is a decentered, rotationally asymmetric surface (a surface with different optical powers depending upon azimuths; a so-called free curved surface).
FIG. 2 is a schematic diagram of the major part of the image observation apparatus using a conventional, coaxial, concave mirror. In the same figure the light from the image information displayed on the display device 61 is reflected by a half mirror 62 and then is made incident to the concave mirror 63. The light reflected by the concave mirror 63 is guided through the half mirror 62 to the observer E. The image information displayed on the display device 61 is formed as an enlarged virtual image by the concave mirror 63. This permits the observer to observe the enlarged virtual image of the image information displayed on the display device 61.
The optical system of the type illustrated in FIG. 1 has such a feature that it is easier to decrease the overall scale of the apparatus and to increase the field of view than in the type using the conventional, coaxial, concave mirror illustrated in FIG. 2.
There are particular desires for the decrease in the scale and weight of the whole apparatus, because the image observation devices such as the head-mounted displays, the goggle type displays, and the like are mounted on the head. Another important issue is to widen the field of view in order to provide the observation of image information displayed on the display means with strong appeal.
In the case of the image observation apparatus such as the head-mounted displays (HMD), the goggle type displays, and the like of the type as illustrated in FIG. 1, where the display device is constructed of a reflective display device (for example, a reflective, ferroelectric, liquid crystal display device), which has a high aperture ratio and which is advantageous in the decrease of scale, it is necessary to interpose an illumination system 70 for illuminating the display device 51 between the display device 51 and the entrance surface 53 of the compact prism 52, as illustrated in FIG. 3.
Here the illumination system 70, for example, has a light source 71, a condenser lens 72 for condensing the light from the light source 71 and converting it into parallel light, a prism 73 including a half mirror surface 73a for reflecting the light from the condenser lens 72 to illuminate the display device 51, and so on. In the image observation apparatus the use of the reflective display element requires the placement of the illumination system for illuminating it between the display device 51 and the compact prism 52 and thus requires increase in the space between the prism 52 and the display device 51, as illustrated in FIG. 3. Therefore, there arise problems that the feature of this type is not taken advantage of and that it is difficult to decrease the size and weight and to increase the field of view.
An object of the present invention is to provide an image display apparatus that permits the observer to observe the image information in a wide field of view and with good image quality while achieving the compactification of the whole apparatus, by properly setting an optical system from light source means to display means (an illumination optical system) and an optical system for guiding the light from the display means to the observer""s eye (a display optical system), in observing the image information displayed on the display means such as a liquid crystal display or the like.
Another object of the present invention is to provide an image display apparatus suitably applicable as a head-mounted display that permits the observer to observe the image information displayed on the liquid crystal display in good order while achieving the compactification of the whole apparatus, by such structure that when the image information displayed on the liquid crystal display is observed using, for example, the reflective liquid crystal display as image display means and using, for example, an optical element having integrally formed surfaces of an entrance surface to which light from the liquid crystal display element is made incident, a decentered, curved, reflecting surface for reflecting the light entering the entrance surface, and an exit surface from which the light from the curved, reflecting surface is made to emerge, as display optical system, an illumination device for illuminating the liquid crystal display is properly set in accordance with the feature of the enlarging display system.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: reflective display means; an illumination optical system for making light from light source means obliquely incident to a display surface of the display means; and a display optical system for guiding light from the display means to an observer to permit the observer to observe image information displayed on the display means, wherein a principal ray emerging from a central part of the display means is emergent obliquely from the display means, the display optical system comprises a decentered, rotationally asymmetric, reflecting surface, the illumination optical system and the display optical system share at least one optical element, and at least one surface of the optical element(s) shared is a curved surface.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: a reflective display device; an illumination optical system for guiding light from light source means to the display device; and a display optical system for guiding the light reflected by the display device to the eye of an observer to allow the observer to observe an image, wherein at least one surface of the display optical system is a decentered, rotationally asymmetric, reflecting surface, a principal ray of display light at a center of a field of view from the display device is emergent at a predetermined angle relative to a normal to a display surface of the display device, the illumination optical system and the display optical system share an optical element, and at least one surface of the optical element is a curved surface.
In one aspect of the present invention, the surface of the optical element is a rotationally asymmetric surface.
In one aspect of the present invention, the optical element comprises a surface acting as a transmitting surface in an optical path of the display optical system and acting as a reflecting surface in an optical path of the illumination optical system.
In one aspect of the present invention, the surface of the optical element acts as a surface having a positive power in both of the display optical system and the illumination optical system.
In one aspect of the present invention, the surface of the optical element is a curved surface.
In one aspect of the present invention, the reflective display device is a ferroelectric liquid crystal display.
An image observation apparatus according to one aspect of the present invention is an image display apparatus wherein light from light source means is guided via a first prism of a single medium having three or more optical surfaces comprising a decentered surface, to illuminate reflective display means obliquely, and light emerging obliquely from the display means is guided via part of the optical surfaces of the first prism and via a second prism of a single medium having three or more optical surfaces comprising a decentered surface to an observer, whereby the observer is allowed to observe image information displayed on the display means.
In one aspect of the present invention, the first prism comprises an entrance surface to which the light from the light source means is incident, a half mirror surface comprised of a rotationally asymmetric surface for reflecting part of light from the entrance surface, and an exit surface from which light reflected by the half mirror surface emerges toward the display means.
In one aspect of the present invention, the light from the display means is incident through the exit surface of the first prism, the light then travels through the half mirror surface and emerges from the first prism, and thereafter the light is incident to the second prism.
In one aspect of the present invention, the second prism comprises an entrance surface to which the light from the half mirror surface of the first prism is incident, a totally reflecting surface for totally reflecting the light from the entrance surface, a reflecting surface comprised of a rotationally asymmetric surface for reflecting the light from the totally reflecting surface, and an exit surface having the same shape as the totally reflecting surface, from which the light from the reflecting surface emerges.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: reflective display means; an illumination optical system for making light from light source means incident to a display surface of the display means; and a display optical system for guiding light from the display means to the pupil of an observer to allow the observer to observe image information displayed on the display means, wherein the illumination optical system guides the light from the light source means via a prism of a triangular prism shape making use of a totally reflecting surface to the display means, the display optical system guides the light from the display means through the totally reflecting surface of the prism to the observer, and an angle between the totally reflecting surface and the display surface of the display means is set so as to satisfy the following condition:
(Dy/Ly)xc2x7Wyxc2x0 less than xcex8 less than 40xc2x0
where Dy represents the diameter of the exit pupil formed by the display optical system in the y-direction, Ly represents an effective image display size in the y-direction, and Wy represents a field of view in the y-direction.
In the image display apparatus according to one aspect of the present invention, a prism vertex angle Pxcex8 of the prism is set to satisfy (Dy/Ly)xc2x7Wyxc2x0 less than Pxcex8 less than 40xc2x0.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: light source means; reflective display means; an illumination optical system for guiding light from the light source means to the display means; a display optical system for guiding the light reflected by the display means to the pupil of an observer and making the observer recognize a virtual image formed thereby as an enlarged image of an image displayed on the display means; and an optical member comprising an optical surface acting to totally reflect light when guiding the light from the light source means to the display means and acting to transmit light when guiding the light reflected by the display means to the pupil, wherein an angle xcex8 between the optical surface and an image display surface of the display means is set to satisfy xcex8 less than 45xc2x0.
In the image display apparatus according to one aspect of the present invention, the display optical system comprises an optical element making use of a plurality of reflecting surfaces and each of the reflecting surfaces forming the optical element is comprised of a surface decentered from a principal ray at a center of a field of view.
In the image display apparatus according to one aspect of the present invention, at least one optical surface forming the optical element is a rotationally asymmetric surface.
In the image display apparatus according to one aspect of the present invention, one of the rotationally asymmetric surfaces comprises an optical surface acting as a totally reflecting surface and also as a transmitting surface.
In the image display apparatus according to one aspect of the present invention, the optical member is comprised of a prism in which an entrance surface, a reflecting surface, and an exit surface are formed integrally, and the light from the light source means is guided into the entrance surface, is reflected by the reflecting surface, and is guided out of the exit surface toward the display means.
In the image display apparatus according to one aspect of the present invention, at least a partial area makes use of total reflection, out of reflection on the reflecting surface of the optical member.
In the image display apparatus according to one aspect of the present invention, the optical member comprises at least one curved surface.
In the image display apparatus according to one aspect of the present invention, the illumination optical system comprises at least one rotationally asymmetric surface.
In the image display apparatus according to one aspect of the present invention, the display means is a ferroelectric liquid crystal panel.
In the image display apparatus according to one aspect of the present invention, the light source means comprises a light source for emitting light of three colors of R, G, and B and the light source means emits the light in synchronism with image display on the display means.
In the image display apparatus according to one aspect of the present invention, the light source comprises LEDs for emitting the light of the three colors of R, G, and B.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: reflective display means; an illumination optical system for making light from light source means incident to a display surface of the display means; and a display optical system for guiding light from the display means to the pupil of an observer to allow the observer to observe image information displayed on the display means, wherein the illumination optical system guides the light from the light source means via an optical member making use of a totally reflecting surface to the display means and the display optical system guides the light from the display means through the totally reflecting surface of the optical member to the observer.
In the image display apparatus according to one aspect of the present invention, the display optical system comprises an optical element making use of a plurality of reflecting surfaces and each of the surfaces forming the optical element is comprised of a surface decentered from a principal ray at a center of a field of view.
In the image display apparatus according to one aspect of the present invention, at least one optical surface forming the optical element is comprised of a rotationally asymmetric surface.
In the image display apparatus according to one aspect of the present invention, one of the rotationally asymmetric surfaces comprises an optical surface acting as a totally reflecting surface and also as a transmitting surface.
In the image display apparatus according to one aspect of the present invention, the optical member is comprised of a prism in which an entrance surface, a reflecting surface, and an exit surface are formed integrally, and the light from the light source means is guided into the entrance surface, is reflected by the reflecting surface, and is guided out of the exit surface toward the display means.
In the image display apparatus according to one aspect of the present invention, at least a partial area makes use of total reflection, out of reflection on the reflecting surface of the optical member.
In the image display apparatus according to one aspect of the present invention, the optical member comprises at least one curved surface.
In the image display apparatus according to one aspect of the present invention, the illumination optical system comprises at least one rotationally asymmetric, curved surface.
In the image display apparatus according to one aspect of the present invention, the display means is a ferroelectric liquid crystal display.
In the image display apparatus according to one aspect of the present invention, the light source means comprises a light source for emitting light of three colors of R, G, and B and the light source means emits the light in synchronism with image display on the display means.
In the image display apparatus according to one aspect of the present invention, the light source comprises LED elements for emitting the light of the three colors of R, G, and B.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: a reflective display element; an illumination optical system for making light from light source means incident to a display surface of the display means; and a display optical system for guiding light from the display means to the pupil of an observer to allow the observer to observe image information displayed on the display means, wherein the display optical system is arranged so as not to interfere with an illumination optical path running from the light source means to the display means and the illumination optical system is arranged so as not to interfere with a display optical path running from the display means to the display optical system.
In the image display apparatus according to one aspect of the present invention, the display optical system comprises a plurality of reflecting surfaces and each of the plurality of reflecting surfaces is comprised of a surface decentered from a principal ray at a center of a field of view.
In the image display apparatus according to one aspect of the present invention, the display optical system comprises an optical surface acting as a totally reflecting surface and also as a transmitting surface.
In the image display apparatus according to one aspect of the present invention, a reflection film is formed in part of the surface functioning as a totally reflecting surface and also as a transmitting surface.
In the image display apparatus according to one aspect of the present invention, at least one optical surface forming the display optical system is comprised of a rotationally asymmetric surface.
In the image display apparatus according to one aspect of the present invention, the reflective display means is a ferroelectric liquid crystal display.
In the image display apparatus according to one aspect of the present invention, polarizing plates whose axes of polarization are approximately perpendicular to each other are placed between the light source means and the display means and between the display means and the display optical system.
In the image display apparatus according to one aspect of the present invention, a ray traveling from the light source means to the display means intersects with a ray traveling from the display means to the display optical system only on the display means.
An image display apparatus according to one aspect of the present invention is an image display apparatus comprising: reflective display means; an illumination optical system for making light from light source means incident to the display means; and a display optical system for guiding light from the display means to an observation position of an observer, the display optical system comprising a plurality of decentered, reflecting surfaces each having an optical power, wherein a principal ray at a center of a field of view, passing a center of an exit pupil of the display optical system, is emergent at a predetermined angle relative to a normal to an image display surface of the display means.
In the image display apparatus according to one aspect of the present invention, the display optical system comprises an optical element in which an entrance surface, a plurality of decentered, curved, reflecting surfaces, and an exit surface are made in surfaces of a material.
In the image display apparatus according to one aspect of the present invention, the decentered, reflecting surfaces each with the optical power forming the display optical system are rotationally asymmetric surfaces.
In the image display apparatus according to one aspect of the present invention, the illumination optical system comprises an optical element having a positive power and being independent of the display optical system.
In the image display apparatus according to one aspect of the present invention, the illumination means turns on light of the three primary colors of R, G, and B in time series in synchronism with image display on the display means, thereby implementing color display.
In the image display apparatus according to one aspect of the present invention, the display means is a ferroelectric liquid crystal panel.
In the image display apparatus according to one aspect of the present invention, the illumination optical system comprises a first polarizing plate for forming illumination light linearly polarized in a predetermined direction and the display optical system comprises a second polarizing plate whose axis of polarization is approximately perpendicular to that of the first polarizing plate.